The present invention generally relates to an end effector for an automated drill and countersink machine, and more particularly to an improved end effector with a shock that mitigates the communication of vibrations to the attached drill tool of the drill and countersink machine in order to increase control of the tool during drilling and countersinking operations.
End effectors are well known and in wide use throughout the aerospace industry as well as other industries. During the assembly of aircraft structures, and in particular during airframe assembly, considerable difficulties may be encountered because various operations, such as drilling and countersinking, need to be performed to extremely fine tolerances.
While various components of the aircraft structure, and in particular the airframes, may constitute a unit durable to considerable stresses once assembly is completed, these individual components may be extremely fragile and need to be handled with great care before assembly.
Various assembly operations, such as drilling and countersinking, may need to be performed to extremely fine tolerances. For example, drilling and countersinking operations may require extreme precision, with tolerances of approximately 20-30 microns in the countersinking depth. The meticulous precision mandated by these operations may impose great difficulties, especially in an industry that depends heavily on mass production. However, these operations may need to be performed with the greatest precision to achieve the highest technological standards possible.
In the past, manual technology was used to conform to the necessary precision required by the drilling and countersinking operation. However, manual drilling and countersinking proved to be a labor intensive process that was carried out one hole at a time. The work was extremely tedious and yet at the same time required a highly skilled operator to consistently produce quality results, and highly skilled quality control inspectors to insure that all the drilled and countersunk holes were flawlessly compatible to corresponding fasteners to meet the specifications of flushness, interference and button formation. These personnel costs substantially increased the costs of the operation and tended to increase the overall expenses of a completed airplane.
The manual process of drilling and countersinking a hole was ready to be replaced by automation, and attempts have been made for many years to obtain the benefits of increased capacity and quality while reducing costs and rework. However, attempts to develop automated drilling and countersinking machines have been hampered by a multitude of practical problems that interfere with the smooth operation of an automated system, resulting in a requirement for continual manual intervention by skilled operators.
Typical automated drill and countersink machines have end effectors that assist in drilling a hole into a workpiece surface as specified by the operator. Although current automated drill and countersink machines are somewhat precise, this particular type of job may require extreme precision, with tolerances of approximately 20-30 microns in the countersinking depth.
Great difficulty may be encountered in achieving such consistent precision due to the vibrations generated by the automated drill and countersink machine when in operation. The end effector is especially susceptible to heavy vibrations because it is the only component of the drill and countersink machine that is in contact with the workpiece surface when the attached drill tool is drilling a hole in the surface. In addition, the automated drill and countersink machine is further subject to vibrations produced by the other components of the machine. Therefore, the attached drill tool of the machine may be exposed to these vibrations, and thus affect the controllability of the tool to carry on an effective drilling and countersinking operation.
The end effector comprises a pressure foot adapted to engage the workpiece surface. Once engaged to the workpiece surface, a rotating chuck attached to the automated drill and countersink machine translates toward the workpiece surface in order to drill and countersink. The impact of the drill tool against the surface during drilling and countersinking operations produces heavy vibrations, which are transferred to the engaged pressure foot. The pressure foot vibrates heavily in response to such transfer from the resulting impact of the drilling and countersinking procedure.
In addition, a spindle motor attached to the automated drill and countersink machine is operative to generate heavy vibrations due to its natural function of producing power to the spindle. The spindle motor is the source of power necessary for the drill and countersink machine to carry out its function. Because the spindle motor supplies kinetic energy to various components of the machine, the spindle motor is in a constant state of motion, thereby producing heavy vibrations in the process.
Thus, there has long been a need in the industry, and in the airframe manufacturing business in particular, for a method and an apparatus for mitigating communication of vibrations to an attached drill tool arising in the process of drilling and countersinking a hole to the required tolerances. In particular, there is a need to eliminate the vibrations generated from the spindle motor and the pressure foot in order to reduce the overall vibrations of the drill and countersink machine.
The present invention addresses and overcomes the above-described deficiency of prior art automated drill and countersink machine by providing a vibration-absorbing end effector wherein a shock is attached to the pressure foot and the pressure foot frame of the end effector. Moreover, the shock may also be attached to the pressure foot and the spindle motor of the machine to mitigate communication of the vibrations to the attached drill tool. In the present end effector of the automated drill and countersink machine, the shock mitigates the communication of vibrations thereby reducing the overall vibration of the machine and increasing control of the drill tool during drilling and countersinking operations. In this respect, not only does the shock mitigate the communications of vibrations generated to the attached tool of the machine, but it also dampens the vibrations at their source.